Carbon nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. Two general types of carbon nanotubes are referred to as multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
Carbon-based nanotubes are being studied for implementation in a variety of applications. These applications include, among others, chemical and bio-type sensing, field-emission sources, selective-molecule grabbing, nano-electronic devices, and a variety of composite materials with enhanced mechanical and electromechanical properties. More specifically, for example, in connection with chemical and biological detection, carbon nanotubes have been studied for applications including medical devices, environmental monitoring, medical/clinical diagnosis and biotechnology for gene mapping and drug discovery. For general information regarding carbon nanotubes, and for specific information regarding SWNTs and their applications, reference may be made generally to “Carbon Nanotubes: Synthesis, Structure, Properties and Applications,” M. S. Dresselhaus, G. Dresselhaus and Ph. Avouris (Eds.), S-Verlag Berlin Heidelberg, New York, 2001; and “T. Single-shell Carbon Nanotubes of 1-nm Diameter,” Iijima, S. & Ichihashi, Nature 363, 603–605 (1993).
Manufacturing processes used to make carbon nanotubes are often characterized by relatively uncontrolled carbon nanotube growth. For example, carbon nanotubes grown from catalyst material often grow in random directions. Where multiple carbon nanotubes are grown in close proximity, the carbon nanotubes often grow into contact with one another, intertwine or otherwise interact in a generally disoriented manner. This nature of grown carbon nanotubes can present challenges to using the nanotubes in a variety of applications.
Nano-magnetic materials and the shrinking bit size of magnetic recording media have increased the demand for analysis or imaging approaches providing high spatial resolution, and in some instances, increased the demand for analysis or imaging of structures exhibiting a high aspect ratio. For instance, Magnetic Force Microscopy (MFM) applications, involving a probe having a magnetic tip mounted on a cantilever, is limited in resolution by the tip's size, shape, and height above the surface of the sample being analyzed. Previously-implemented MFM probes include focused ion beam (FIB) milled sharp tips, suitable for sub-30 nm wide one dimensional features; tips with an FIB-drilled hole, suitable for imaging 50 nm transitions on a hard drive; tips with magnetic dots deposited through stencil masks, suitable for imaging features with 42 nm FWHM; and electron beam deposition (EBD) tips. Other applications have involved the use of nanotube-based MFM tips with magnetic catalyst particles to image 85 nm features; however, these approaches involving nanotube tips are generally unsuitable for topography, and the amount of magnetic material at the tip is not readily controllable.
Difficulties associated with the above discussion have presented challenges to nanotube applications, including the manufacture of nanotubes and their implementation in a variety of applications.